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Aerobraking is the transition from the initial elliptical orbit to the science orbit where
Odyssey will circle Mars at a uniform altitude. It is a technique that slows the space-craft
down by using frictional drag as it flies through the upper part of the planet's
atmosphere.
During each of its long, elliptical loops around Mars, the orbiter will pass through the
upper layers of the atmosphere each time it makes its closest approach to the planet.
Friction from the atmosphere on the spacecraft and its wing-like solar array will cause
the spacecraft to lose some of its momentum during each close approach, known as
an "a drag pass." As the spacecraft slows during each close approach, the orbit will
gradually lower and circularize.
Aerobraking will occur in three primary phases that engineeers call walk-in, the main
phase and walk-out. The walk-in phase occurs during the first four to eight orbits following
Mars arrival. The main aerobraking phase begins once the point of the space-craft's
closest approach to the planet, know as the orbit's "periapsis," has been low-ered
to within about 100 kilometers (60 miles) above the Martian surface. As the
spacecraft's orbit is reduced and circularized during approximately 273 drag passes in
76 days, the periapsis will moved northward, almost directly over Mars' north pole.
Small thruster firings when the spacecraft is at its most distant point from the planet will
keep the drag pass altitude at the desired level to limit heating and dynamic pressure
on the orbiter. The walk-out phase occurs during the last few days of aerobraking
when the period of the spacecraft's orbit is the shortest.
Related Links: Focus on 2001 Mars Odyssey, SpaceRef
2001 Mars Odyssey Mission Overview, SpaceRef |
